The Infiniband® network includes nodes that communicate through a channel-based switched fabric (Infiniband® is a registered trademark of Infiniband Trade Association, located in Beaverton, Oreg.). For example, the nodes may be a host, an input/output subsystem, or a router which connects to another network. The switched fabric is made up of a collection of switches, routers, and/or links that connect a set of channel adapters. The channel adapters form an interface between the switched fabric and the nodes. The channel adapter of the host is referred to as a host channel adapter. The channel adapter of an I/O subsystem is referred to as a target channel adapter.
In Infiniband®, two processes communicate using queue pairs. Each of the processes has a queue pair configured to communicate with the queue pair of the other process. A queue pair includes a send queue and a receive queue. Specifically, in order for a process to send a message to another process, the process posts the message to the send queue. The host channel adapter sends the message in the form of packets to the channel adapter having the receive queue. To enable multiple processes to simultaneously communicate using the same hardware, it is necessary to quickly switch between queue pairs. To facilitate this, the connection metadata that a queue pair requires to function is stored in a data structure known as a queue pair state. A queue pair state allows the hardware to quickly switch between different connections by accessing the information stored in different queue pair states.